<!-- 开发环境版本，包含了有帮助的命令行警告 -->
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>

<div id="example-4">
<input
  type="radio"
  v-model="pick"
  v-bind:value="a">
<span>{{ pick }}</span>
</div>

<script>
var vm = new Vue({
  el: '#example-4',
  data: {
    pick: 'default',
	a: 'v'
  }
})

//当选中时，取vm.a的值赋给pick
//即，vm.pick === vm.a


</script>